The present invention relates to a crosslinked product of an unsaturated carboxylic acid-based copolymer, precisely to a crosslinked product of an unsaturated carboxylic acid-based copolymer having good water absorbability and biodegradability, and to a method for producing it. The invention also relates to a novel unsaturated carboxylic acid polymer, precisely to an unsaturated carboxylic acid polymer having good properties of high detergency and biodegradability, and to its use, as well as to a biodegradable builder, a detergent composition and a dispersant containing the polymer as the constituent ingredient.
Absorbent resin can absorb water of tens to thousands times the self-weight of the resin, and is widely used in various fields of sanitary napkins, cut-off materials, soil improvers, water-holding materials, oil-water separators, dirty water absorbents, etc. After used, absorbent resin is disposed of in soil or is incinerated. However, thus discarding the used absorbent resin is problematic in that it still remains in soil without being degraded therein and in that, after incinerated, it is strongly alkaline to cause damage to incinerators. To solve the problems, various biodegradable absorbent resins have been proposed, and starch-based resins, hyaluronic acid-based resins, polyaspartic acid-based crosslinked products and polyglutamic acid-based crosslinked products are known of those, polyglutamic acid-based crosslinked products have especially excellent biodegradability (for example, Japanese Patent Laid-Open Nos. 322358/1994, 300563/1995, 251402/1998). However, their production methods are all complicated and are not efficient.
The first aspect of the present invention has been made from the viewpoint as above, and its object is to provide a crosslinked product of a carboxylic acid-based copolymer having good water absorbability and biodegradability and to provide an efficient method for producing it.
Conventional detergent comprising surfactant as an essential ingredient contains a builder as an auxiliary component to the surfactant to thereby improve its detergency. As the builder, known are inorganic compounds which are alkaline in water, and polymers of unsaturated aliphatic carboxylic acids, etc. As examples of the former, mentioned are sodium and potassium carbonates, hydrogencarbonates, phosphates, polyphosphates and silicates, as well as zeolite, etc.; while examples of the latter include polyacrylic acid, polymaleic acid, polyitaconic acid, etc.
Of those builders, much used are phosphates, polyphosphates and zeolite, as they are effective in detergent, economical and easy to handle. However, these are problematic from the viewpoint of the protection of the global environment in that phosphates and polyphosphates eutrophicate lakes, marshes and rivers while zeolite precipitates in rivers, etc.
Accordingly, it is desired to develop some other builders, of which the capability, especially, the chelating ability (calcium ion-sequestering ability) is good like that of conventional builders, which are well biodegradable to be gentle to the environment, without remaining for a long period of time on the earth, and are therefore not problematic from the viewpoint of the protection of the global environment, and which are economical.
To meet the requirements, Japanese Patent Laid-Open No. 239127/1993 discloses chelatable and biodegradable, crosslinked polymers suitable for builders. To prepare the polymers, water-soluble oligomers, which contain biodegradable low-molecular-weight components, are crosslinked at their main chains with a crosslinking agent, such as polyethylene glycol, citric acid, tartaric acid or the like, via a biodegradable ester or amido group to thereby increase their molecular weight. However, though having a low molecular weight thereby to have increased biodegradability, the linear polyacrylic acid moiety in those crosslinked polymers is hardly biodegradable, and, in addition, the polymers contain hardly-biodegradable high-molecular-weight linear polyacrylic acids to no small extent. Therefore, the biodegradability of the crosslinked polymers disclosed is not satisfactory. Another problem with the polymers is that the method for producing them is not simple, as requiring two steps, one for polymerizing the oligomer and the other for crosslinking the polymerized oligomer, and requiring the special crosslinking agent.
Japanese Patent Laid-Open No. 80377/1975 discloses acrylic acid or acrolein polymers and their modified derivatives or copolymers usable as builders. However, these are all problematic in that their chelatability and biodegradability are not satisfactory.
Accordingly, it is desired to develop polymers having good chelatability and good biodegradability and therefore suitable to builders and to develop methods for efficiently producing them.
In the field of dispersants for inorganic pigments, sodium polyacrylate or the like is used for lowering the viscosity of slurry dispersions and for improving the viscosity stability thereof. However, polyacrylic acid is not biodegradable. Also in this field, therefore, it is desired to develop some other dispersants which are biodegradable without remaining on the earth for a long period of time and which are economical.
The second to fourth aspects of the invention are to provide an unsaturated carboxylic acid polymer having good chelatability and good biodegradability and therefore suitable to builders, and to provide a builder for detergent, a detergent composition and a dispersant containing the polymer.
We, the present inventors have assiduously studied, and, as a result, have found out a crosslinked product of a specific unsaturated carboxylic acid-based copolymer which is derived from a monomer component that comprises an unsaturated monocarboxylic acid monomer and a quinone. On the basis of this finding, we have completed the first aspect of the invention.
Specifically, the first aspect of the invention is summarized as follows:
(1) A crosslinked product of an unsaturated carboxylic acid-based copolymer derived from a monomer component that comprises an unsaturated monocarboxylic acid monomer and a quinone, of which the copolymer contains from 1 to 10 mol % of the quinone.
(2) The crosslinked product of an unsaturated carboxylic acid-based copolymer of above (1), for which the unsaturated monocarboxylic monomer is an acrylic or methacrylic acid, or its salt.
(3) The crosslinked product of an unsaturated carboxylic acid-based copolymer of above (1) or (2), for which the quinone is at least one selected from hydroquinone, resorcinol, catechol, naphthalenediol, anthraquinol, benzoquinone, naphthoquinone, anthraquinone, and their substituted derivatives.
(4) The crosslinked product of an unsaturated carboxylic acid-based copolymer of any of above (1) to (3), which is a biodegradable absorbent resin.
(5) A method for producing the crosslinked product of an unsaturated carboxylic acid-based copolymer of any of above (1) to (4), which comprises heating an unsaturated monocarboxylic acid monomer, a quinone and a crosslinking agent in an aqueous solvent in the presence of an initiator, and in which the quinone accounts for from 1 to 10 mol % of the overall amount of the monomer component.
(6) The method of above (5) for producing the crosslinked product of an unsaturated carboxylic acid-based copolymer, wherein the crosslinking agent is a water-soluble compound having, in one molecule, at least two hydroxyl groups, amino groups or unsaturated groups capable of reacting with a carboxyl group.
We, the present inventors have further found that an unsaturated carboxylic acid polymer having a specific chemical structure is soluble in water, well chelatable and biodegradable, and that the polymer is highly useful for builders, detergent compositions and dispersants. On the basis of these findings, we have completed the second to fourth aspects of the present invention.
Specifically, the second aspect of the invention is summarized as follows:
[1] An unsaturated carboxylic acid polymer, (a) which gives, in proton nuclear magnetic resonance spectrometry, absorption peaks at least at xcex4 of from 6.4 to 7.5 ppm and at xcex4 of from 1.0 to 3.2 ppm, and gives a ratio of the integrated value of the peak area at xcex4 of from 6.4 to 7.5 ppm to that of the peak area at xcex4 of from 1.0 to 3.2 ppm of falling between 2.2xc3x9710xe2x88x923 and 0.3, (b) which has a number-average molecular weight of from 500 to 1,000,000, (c) which is soluble in water, and (d) which has a degree of calcium ion-sequestering ability of at least 150 mg CaCO3/g.
[2] A biodegradable builder containing, as the constituent ingredient, the unsaturated carboxylic acid polymer of above [1].
[3] A detergent composition containing, as the constituent ingredients, the unsaturated carboxylic acid polymer of above [1] and a surfactant.
[4] A dispersant which comprises a polymer prepared by neutralizing the unsaturated carboxylic acid polymer of above [1] with an alkali.
The third aspect of the invention is summarized as follows:
[1] An unsaturated carboxylic acid polymer, which comprises;
(A) from 30 to 99 mol % of repetitive units (a) of a general formula [III-1]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group,
(B) from 0 to 69.9 mol % of repetitive units (b) of a general formula [III-2]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and
(C) from 0.1 to 50 mol % of structural units that are the total of repetitive units (c) of a general formula [III-3]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and W represents a hydrogen atom or an alkali metal atom,
repetitive units (d) of a general formula [III-4]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and W represents a hydrogen atom or an alkali metal atom, and
repetitive units (e) of a general formula [III-5]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and W represents a hydrogen atom or an alkali metal atom, and
which has a number-average molecular weight of from 500 to 1,000,000.
[2] An unsaturated carboxylic acid polymer, which comprises;
(A) from 30 to 99 mol % of repetitive units (a) of a general formula [III-1]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group,
(B) from 0 to 69.9 mol % of repetitive units (b) of a general formula [III-2]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and
(C) from 0.1 to 50 mol % of structural units that are the total of repetitive units (cxe2x80x2) of a general formula [III-3xe2x80x2]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and W represents a hydrogen atom or an alkali metal atom,
repetitive units (dxe2x80x2) of a general formula [III-4xe2x80x2]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and W represents a hydrogen atom or an alkali metal atom, and
repetitive units (exe2x80x2) of a general formula [III-5xe2x80x2]: 
wherein X represents a hydrogen atom, an alkali metal atom or an ammonium group, and W represents a hydrogen atom or an alkali metal atom, and
which has a number-average molecular weight of from 500 to 1,000,000.
[3] A biodegradable builder containing, as the constituent ingredient, the unsaturated carboxylic acid polymer of above [1] or [2].
[4] A detergent composition containing, as the constituent ingredients, the unsaturated carboxylic acid polymer of above [1] or [2] and a surfactant.
[5] A dispersant which comprises a polymer prepared by neutralizing the unsaturated carboxylic acid polymer of above [1] or [2] with an alkali.
The fourth aspect of the invention is summarized as follows:
[1] An unsaturated carboxylic acid polymer, which comprises;
(A) repetitive units (a) of a formula [IV-1]:
xe2x80x94(CH2)xe2x80x94xe2x80x83xe2x80x83[IV-1],
(B) repetitive units (b) of a general formula [IV-2]: 
wherein R1 represents a hydrogen atom or a methyl group; X represents a hydrogen atom, an alkali metal atom or an ammonium group, and
(C) repetitive units (c) of a general formula [IV-3]: 
wherein R2 represents a hydrogen atom or a methyl group; W represents a hydrogen atom or an alkali metal atom,
with the structural units of the repetitive units (c) accounting for from 0.25 to 50 mol % of all the structural units of the polymer, and
which has a number-average molecular weight of from 500 to 1,000,000.
[2] An unsaturated carboxylic acid polymer, which comprises;
(A) repetitive units (a) of a formula [IV-1]:
xe2x80x94(CH2)xe2x80x94xe2x80x83xe2x80x83[IV-1],
(B) repetitive units (b) of a general formula [IV-2]: 
wherein R1 represents a hydrogen atom or a methyl group; X represents a hydrogen atom, an alkali metal atom or an ammonium group, and
(C) repetitive units (cxe2x80x2) of a general formula [IV-3xe2x80x2]: 
wherein R2 represents a hydrogen atom or a methyl group,
with the structural units of the repetitive units (cxe2x80x2) accounting for from 0.25 to 50 mol % of all the structural units of the polymer, and
which has a number-average molecular weight of from 500 to 1,000,000.
[3] A method for producing the unsaturated carboxylic acid polymer of above [1], which comprises copolymerizing one or more of unsaturated carboxylic acids or their salts of a general formula [IV-4]: 
wherein R3 represents a hydrogen atom or a methyl group; X represents a hydrogen atom, an alkali metal atom or an ammonium group; and Y represents a hydrogen atom or a group of COOX, with an unsaturated compound of a general formula [IV-5]: 
wherein R4 represents a hydrogen atom or a methyl group; Y represents a hydrogen atom or a group of COOX (in which X represents a hydrogen atom, an alkali metal atom or an ammonium group); and W represents a hydrogen atom or an alkali metal atom, in the presence of a polymerization initiator.
[4] A method for producing the unsaturated carboxylic acid polymer of above [2], which comprises copolymerizing one or more of unsaturated carboxylic acids or their salts of a general formula [IV-4]: 
wherein R3 represents a hydrogen atom or a methyl group; X represents a hydrogen atom, an alkali metal atom or an ammonium group; and Y represents a hydrogen atom or a group of COOX, with an unsaturated compound of a general formula [IV-5xe2x80x2]: 
wherein R4 represents a hydrogen atom or a methyl group; Y represents a hydrogen atom or a group of COOX (in which X represents a hydrogen atom, an alkali metal atom or an ammonium group), in the presence of a polymerization initiator.
[5] A biodegradable builder containing, as the constituent ingredient, the unsaturated carboxylic acid polymer of above [1] or [2].
[6] A detergent composition containing, as the constituent ingredients, the unsaturated carboxylic acid polymer of above [1] or [2] and a surfactant.
[7] A dispersant which comprises a polymer prepared by neutralizing the unsaturated carboxylic acid polymer of above [1] or [2] with an alkali.